The present invention relates to an apparatus for depositing air-suspended fibers on a wire to produce a substantially plane fibrous web on the wire, apparatus being provided with at least one distributor which comprises a housing, means for supplying fibers, and at least two parallel rows of impellers which rotate, when in use, around an axis which is substantially perpendicular to the wire, the impellers being situated between the supply means and a net behind which the wire is provided in such a manner that the fibers will flow from the supply means via the impellers and the net to the wire.
In the production of napkins and new sanitary products, especially sanitary towels for women and incontinent persons, the possibilities of producing increasingly thin products have increased in recent years. The consumers of course demand that these napkins or sanitary towels have the same absorbency as the previously known, more solid products. Therefore, it is essential to maintain a homogeneous product quality as the product is more optimized in thickness than it was previously. For the manufacture of products of the above-mentioned type, the web is subsequently cut into narrow strips which are used in the final products. The manufacturer of such final products demands that the strips cut from the web have a homogeneous thickness in order to secure homogeneous product quality. Homogeneous product quality is not only vital to the properties of the products in subsequent treatment, but also in order to secure that the products will occupy the very same volume when packed and not more or less of the packaging volume for the same amount of products.
GB 2,008,638 and DK 144,382 disclose such an apparatus with several, preferably four, parallel rows of rotating impellers. The rows form a 90.degree. angle on the axis along which a wire below extends, and each of the rotating impellers rotates in its own section of the distributor. A net is situated between the impellers and the wire. This causes a sausage-shaped body of fibers to be formed between the parallel rows, the fibers falling or being sucked gradually from the body down through the net and onto the wire. It appears, however, that problems arise related to keeping a homogeneous thickness profile over the fibrous layer formed on the wire.
SE 467,740 discloses an apparatus that seeks to remedy the above problem. The apparatus used corresponds to the apparatus disclosed in the above-mentioned British and Danish publications. The difference consists in the use of a special net with different mesh sizes. The mesh size is larger under the impellers as it has been found that the fibrous layer formed on the wire, especially in the area below the center of the impellers, will be thinner than elsewhere in the fibrous layer. The disadvantage of the manner in which the Swedish publication seeks to achieve a homogeneous thickness of the fibrous layer on the wire is that it is difficult and involves large expenditures to produce the nets with different mesh sizes. Furthermore, it is necessary to use different nets depending on the types of fibers used for the production of the fibrous layer, and similarly the choice of mesh sizes depends on the size and the density of the fibers.
As it appears, the use of the prior art apparatuses has made it difficult to maintain a sufficiently homogeneous product quality because the fibrous layer formed on the wire does not possess the homogeneity of thickness that is required. This has caused the products within the same production line to fail to have the same properties. Besides, the non-homogeneous thickness of the products has had the disadvantage that the product packaging, which has also been optimized along with the optimization of the products, is bigger than necessary in some cases and too small in other cases.
Thus, it is the object of the present invention to minimize the above-mentioned disadvantages and provide an apparatus for the production of a fibrous web on a wire in which the layer thickness is homogeneous throughout the web.